1. Field of the Invention
The present invention relates to a charged particle beam apparatus, a charged particle beam irradiation method, and a method of manufacturing a semiconductor device.
More specifically, the present invention relates to a charged particle beam apparatus to, for example, scan a specimen with a charged particle beam, with a position on the specimen to be irradiated being beforehand designated, to a charged particle beam irradiation method, and to a method of manufacturing a semiconductor device which includes, for example, measuring the specimen with the use of the irradiation method.
2. Related Background Art
When a charged particle beam irradiation apparatus such as a scanning electron microscope (SEM) is used to observe a specimen, raster scanning is performed while controlling a trajectory of an electron beam from an electron gun using a scanning deflector. A secondary electron or a reflected electron generated from the surface layer of the specimen by irradiation with the electron beam is detected to acquire an image of the surface of the specimen from the detected signal. Characteristics of the raster scanning lie in that an irradiation position of the electron beam continuously moves in one direction.
However, when portions having concave/convex shapes and differences in materials in an LSI pattern are scanned with the electron beams, a phenomenon called as charge-up occurs in the specimen depending on the pattern shape or the scanning direction of the electron beams, and contrast sometimes fluctuates in an image due to the charge-up. Furthermore, sometimes a difference occurs in contrast or image resolution between an edge portion having an edge crossing at right angles to the scanning direction of the electron beams and an edge portion having an edge extending in parallel with the direction of the electron beams.
Regarding a conventional line pattern, its image is acquired in such a manner that the scanning direction of the electron beams crosses at right angles to the edge of the pattern. Therefore, the contrast or resolution of the edge portion does not especially raise any problem. However, in recent years, sufficient shape evaluation and process management have been impossible only with one-dimensional measurement of line patterns because of integration and complication of the LSI pattern. Therefore, evaluation of two-dimensional shape has been executed with the use of two-dimensional image information obtained by the raster scanning.
However, as described above, the raster scanning sometimes still causes contrast fluctuations depending on the pattern shape or- the scanning direction, and changes of the resolution by the direction of the edge. Therefore, when the shape is two-dimensionally measured from the image obtained by the raster scanning, measurement results including an influence of the scanning direction are outputted. In order to obtain an image from which the influence of the scanning direction is removed, there are required scanning methods other than the raster scanning.
Examples of a scanning method involving little influence of the scanning direction include random scanning disclosed, for example, in Japanese Patent Application Laid-Open (kokai) No. 5-151921. The invention of the Japanese Patent Application Laid-Open No. 5-151921 is characterized in that an irradiation position information signal designating an electron beam irradiation position in a scanning plane scanned by the electron beam is successively outputted so that the irradiation positions are designated at random to each other, and the irradiation position corresponding to the outputted irradiation position information signal is sequentially irradiated with the electron beams.
However, when a whole irradiation region is scanned with the electron beams at random, a very long time is required to obtain the image for the measurement depending on the magnification of the measurement. Furthermore, there has been a problem that a sufficient S/N cannot be secured due to the discrete beam irradiation as compared with the continuous beam irradiation in the raster scanning.